In certain high speed rotating equipment with static excitation, such as large turbine-generator systems, carbon brush current collection systems are utilized to conduct a field current to the generator rotor. The collector sets typically comprise a pair of collector rings, or one for each pole, mounted on the rotor and a set of stationary brushes angularly displaced around, and in contact with, each collector ring. In order to protect the collector sets and to prevent inadvertent contact with them by personnel, the collector sets are enclosed within an enclosure which includes a fixed base. This enclosure is commonly referred to as a collector house. Typically the collector house includes stationary traverse end walls having sealed openings through which the rotor shaft passes and a house defining the roof and sidewalls of the enclosure. In some installations, it is desirable to be able to change the brushes without shutting the generator down. Accordingly, the housing is provided with doors through which access may be gained to the collector set.
Because of high demands, it is common to arrange a plurality of carbon brushes within a magazine-type brush holder. Several brushes, typically about six, are grouped within the brush holder which are arranged around the outside diameter of the generator rotor. Examples of such brush holders are described in U.S. Pat. No. 3,387,155, issued on June 4, 1968, and U.S. Pat. No. 3,710,478 which issued on Jan 16, 1973.
While these devices permit ease of brush replacement, it must first be determined when one or more brushes has become worn to the point that it must be replaced. Typically, this is done by a visual inspection of the brushes on a periodic basis. The collector environment inside the house is relatively noisy, and contains high speed rotating equipment operating at high voltages. Thus, an inspector, in order to visually inspect for worn brushes, must enter a relatively hostile environment while the generator is .operating. Such inspections are done while the generator is on-line, in order to minimize the costly down time of the power generation system. What is needed then is a device whereby a worn brush condition can be indicated to an operator located at a remote location, to obviate the need of placing maintenance personnel within the collector house to conduct brush inspections while the generator is on-line.